A VAV box’s binary air flow relief object (VavSuAirFlRlf) can be set to True by the air handling unit. This is done to relieve flow resistance in the duct system in order to maintain proper static pressure. The VAV controller responds by increasing its air flow setpoint (VavSuSpAirFl).
When device mode = control mode and both EnRlf (Enable relief) and VavSuAirFlRlf equal On, VavSuSpAirFl will be set to the maximum of either its current value or the parameter AirFlRlf.
NOTE:
Relief has no effect on the supply chain VAV air demand signal VavSuAirDmd.